Using multicarrier or carrier aggregation (CA) operations, wireless devices in an LTE network may be able to receive and/or transmit data from/to more than one serving cells. FIGS. 1A-1B are schematic diagrams illustrating example carrier aggregation scenarios. Specifically, FIG. 1A illustrates an example network system 100 that includes a wireless device 110 that is able to receive and/or transmit data to a network node 115 via two uplink (UL) and two downlink (DL) inter-band component carriers (CC). FIG. 1B illustrates an example network system 150 that includes wireless device 110 being able to receive and/or transmit data to network node 115 via three uplink (UL) and two downlink (DL) inter-band component carriers (CC).
In general, a CA-capable wireless device 110 can be configured to operate with more than one serving cells. The carrier of each serving cell is generally called as a component carrier (CC). The component carrier (CC) means an individual carrier in a multi-carrier system. The term carrier aggregation (CA) is also called (e.g. interchangeably called) “multi-carrier system,” “multi-cell operation,” “multi-carrier operation,” “multi-carrier” transmission and/or reception. A wireless device 110 may be interchangeably called user equipment (UE).
CA is used for transmission of signaling and data in the uplink and downlink directions. One of the CCs is the primary component carrier (PCC) or primary carrier or anchor carrier. The remaining CCs may be called secondary component carriers (SCCs) or secondary carriers or supplementary carriers. The serving cell may be interchangeably called a primary cell (PCell) or primary serving cell (PSC). The secondary serving cell may be interchangeably called a secondary cell (SCell) or secondary serving cell (SSC).
The PCC or anchor CC can carry the essential wireless device-specific signaling. The PCC (or PCell) exists in both uplink and downlink directions in CA. Where there is a single UL CC, the PCell uses that CC. The network node 115 may assign different primary carriers to different wireless devices 110 operating in the same sector or cell.
FIG. 2 is a schematic diagram illustrating an example network 200 including wireless devices deploying dual-connectivity. Similar to CA, dual connectivity also provides a way for aggregating multiple carriers from independent transmission nodes 115 to any wireless device 110. Dual Connectivity (DC) refers to the operation where a given wireless device 110 consumes radio resources provided by at least two different network points. In certain embodiments, the network points may include a main network node 115A and a secondary network node (SeNB) 115B. In certain embodiments, the main network node 115A may include a main eNodeB (MeNB), and the secondary network node 115B may include a secondary eNodeB (SeNB). The main network node 115A and the secondary network node 115B are connected with non-ideal backhaul 210A while in RRC_CONNECTED. Wireless device 110A in dual connectivity maintains simultaneous connections to main network node 115A and secondary network node 115B. Main network node 115A may be referred to as an anchor node, and the secondary network node 115B may be referred to as a booster node.
As the name implies, the main network node 115A controls the connection and handover of secondary network node 115B. No secondary network node 115B standalone handover is defined for Rel-12. Thus, signaling by the MeNB is needed for SeNB changes. Both the anchor node and booster node are able terminate the control plane connection towards wireless device 110A and may, thus, be the controlling nodes of wireless device 110A, in certain embodiments.
Contrary to CA, dual connectivity involves independent transmission from different network nodes 115A and 115B to any wireless device 110A. At least one cell 212A of both main network node 115A and secondary network node 115B contains both UL and DL. The cell having both UL and DL may be identified as the PCell for main network node 212A and the PSCell for secondary network node 115B. There may be more secondary cells (SCell) attached to either main network node 115A and/or secondary network node 115B.
In the example embodiment depicted in FIG. 2, only one secondary network node 115B is connected to wireless device 110A. However, it is recognized that more than one secondary network node 115B may serve wireless device 110A. Typically, wireless device 110A is configured with at least a PCC from main network node 115A and also a PCC from secondary network node 115B. The primary serving cells on PCCs from main network node 115A and secondary network node 115B are generally called the PCell and PSCell, respectively. Wireless device 110A may also be configured with one or more SCCs from main network node 115A and secondary network node 115B. The serving cell on SCC may be called as secondary serving cell (SCell). Additionally, the PCell and PSCell typically operate or serve wireless device 110A independently. As shown in FIG. 2, dual connectivity is a wireless device-specific feature and network node 115A-B may support a dual connected wireless device 110A and a legacy UE 110B at the same time.
Interference between UL and DL may occur when an frequency division duplex (FDD) system operates next to a time division duplex (TDD) system in adjacent bands. FIG. 3 illustrates a schematic diagram illustrating the operation of a FDD system 302 next to a TDD system 304 in the adjacent bands. Specifically, FIG. 3 illustrates an example scenario wherein a FDD system 302 operates in E-UTRA band 7 in 2.6 GHz adjacent to a TDD system 304 operating in E-UTRA band 38 in 2.6 GHz. The FDD and TDD systems in these bands (band 7 and band 38 respectively) may use carriers which are next to each other. As such, if an FDD system operates in the same geographical area with a TDD system when the TDD and FDD carriers are close the edge of the bands, then UL-DL interference may occur. Even perfect time synchronization of the systems may not avoid the UL-DL interference, in certain embodiments.
In contrast to TDD-TDD adjacent device-to-device (UE-to-UE) interference in the same band, a band select filter may improve the receiver blocking performance in case of TDD-FDD operated in adjacent bands, such as the scenario described below with respect to FIG. 8. Accordingly, additional isolation due to band select filter and also assumed guard bands 306 in both edges of the TDD band 304 may result in comparably favorable situation for TDD/FDD in adjacent bands case as compared to TDD/TDD in the same band case. In the example scenario of FIG. 3, guard bands 306 of 10 MHz are employed between FDD system 302 and TDD system 304.
When an UL transmission interferes with a DL reception and/or a DL transmission interferes with an UL reception, UE-to-UE interference and/or base station to base station (BS-to-BS) interference may occur. This occurs in addition to base station-to-device (BS-to-UE) and device-to-base station (UE-to-BS) adjacent channel interferences similar to FDD/FDD coexistence scenario. The UE-to-UE and BS-to-BS interference problems for band 7 and band 38 in the same geographical area are shown in FIG. 4 and FIG. 5, respectively. Specifically, FIG. 4 is a schematic diagram of a system 400 that may experience UE-to-UE interference between TDD and FDD in 2600 MHz bands. Similarly, FIG. 5 is a schematic diagram of a system 500 that may experience BS-to-BS interference between TDD and FDD in 2600 MHz bands.
BS-to-BS interference can be handled with band specific filters, site solutions and guard bands. It may be a “simple” deterministic problem in certain deployment scenarios wherein carrier and/or operator specific filters can be implemented at the BS side. However, UE-to-UE interference is more challenging to handle with filters. Unlike a BS-to-BS interference case, special filter solutions at the wireless device may be infeasible due to cost, size, etc. Additionally, when a wireless device is roaming, the wireless device may need to transmit and receive in many other bands (compared to home operator bands), which may also increase the filter design costs.
For at least these reasons, TDD/FDD adjacent channel interference such as that shown for the bands shown in FIG. 1 may continue to be an issue where FDD and TDD systems cannot be coordinated. Stated differently, UL to DL interference remain an issue for FDD and TDD adjacent systems and is likely to be handled by band select filters since other solutions than coordination may be required.
Adjacent channel interference may also be an issue between two TDD systems. In certain embodiments, two TDD systems may be operated using TDD synchronization (i.e. time-alignment) and UL to DL coordination to avoid TDD-TDD adjacent channel interference. More specifically, these techniques may be employed to avoid interference between UL and DL slots. However, such techniques may require coordination between operators. Specifically, when TDD configurations used in two different cells operating in the band edges of two neighboring TDD bands are not coordinated, then BS-to-BS interference and UE-to-UE interference may occur. This is similar to the TDD-FDD case described above. FIG. 6 is a schematic diagram illustrating the potential for BS-to-BS interference and UE-to-UE interference caused by TDD-TDD adjacent bad operations. More specifically, FIG. 6 illustrates the potential interference resulting from the operation of wireless device 610A and network node 615A in band 42 and wireless device 610B and network node 615B in band 43.
The occurrence of UE-to-UE interference may adversely impact the operation of the transceiver of the wireless device 610A-610B. For example, UE-to-UE interference may result in transmitter leakage and/or receiver blocking that may cause the wireless device 610A-610B not able to function properly. FIG. 7 is schematic diagram illustrating transmitter leakage of signals into the victim receiver in a system 700. FIG. 8 is a schematic diagram illustrating receiver blocking in a system 800. Still another adverse impact of UE-to-UE interference may be that one of the primary benefits of TDD (i.e. configurable UL to DL asymmetry) may be hampered.
LTE operation may soon expand to the unlicensed band. Allowing unlicensed access for LTE systems may provide certain advantages. For example, an LTE FDD and/or TDD carrier may be aggregated with an LTE carrier in the unlicensed band. The unlicensed carrier may be either in FDD Supplemental Downlink (SDL) or in TDD fashion. SDL carrier is a DL only carrier which is used only as a secondary cell (SCell) with a primary cell (PCell). In certain embodiments, when one or more licensed LTE carriers are aggregated with one or more unlicensed LTE carriers, then the unlicensed LTE band is referred to as an LAA band. LAA may also be employed with Dual Connectivity, wherein aggregation is done based on Dual Connectivity principles rather than Carrier Aggregation principles. Still another advantage may be that stand-alone unlicensed LTE access may be enabled. Specifically, two LTE carriers in unlicensed bands can be aggregated either in CA or in DC manner.
Similar situation as described for TDD-FDD and TDD-TDD cases can also arise when operating in CA involving FDD/TDD frequency bands with unlicensed bands, as for unlicensed bands possibly DL only operation or TDD operation can apply in different time instances.
As mentioned briefly above, adjacent channel interference may negatively impact the transceiver of a wireless device. For example, adjacent channel interference may result in transmitter-side imperfections. Specifically, transmitter emissions within the receiver band may result due to out-of-band (OOB) or spurious emissions. As depicted in FIG. 7, unwanted transmitter emissions falling within receiver channel cannot be suppressed by receiver channel select filters. Thus, the OOB emissions from aggressor wireless devices towards the victim receivers add to total interference levels in the baseband.
OOB emissions may be defined in two ways. First, OBB emissions may be defined by Spectrum emission mask (SEM). Second, OBB emissions may be defined by Adjacent channel leakage ratios (ACLR). Both SEM and ACLR are ways to measure the performance of a transmitter. SEM provides the mechanism for suppression of unwanted power outside the carrier bandwidth, while the ACLR measures the exact amount of power that can be ‘leaked’ into adjacent channels. In LTE specifications, SEM has a much narrower reference bandwidth than ACLR. In LTE requirements, ACLR gives stricter performance requirement than SEM. A such, satisfying ACLR requirements would also satisfy SEM requirements.
Adjacent channel interference may also result in receiver-side imperfections, in certain embodiments. For example, imperfect receiver-side filtering may result in a strong interfering signal at an adjacent channel, which can in turn cause the receiver of a victim wireless device 110 to be desensitized. Increased desensitization levels cause a receiver to become blocked, which may be referred to as receiver blocking.
As noted above, FIG. 8 illustrates the impact of strong interfering signals at the victim receiver due to imperfect receiver filtering. Strong interference signals 802 from adjacent channel transmission saturates receiver front-end 804 before RX channel filtering 806. This phenomenon takes place after the band selective filter 808, so even a guard band (within the band) will not help mitigate the interference.
In case of TDD and FDD systems operating in different bands, the band select filter 808 will provide some additional isolation between TDD and FDD systems, thus the receiver blocking performance will be improved.
In certain embodiments, the wireless device may be barred to access a cell or may be barred for accessing certain type of services. For example, a wireless device may be barred from accessing MBMS, video calls, voice calls, or other services. To enable access barring, the cell transmits access barring information in a system information (SI) message. For example, the access barring information may be transmitted in an SIB2 message in LTE. Before selecting a cell, a wireless device in idle state reads the SI message. If the SI message includes access barring information, the wireless device may not reselect that cell. Similarly, a current serving cell will not handover a wireless device to a target cell where access barring is enabled if the serving cell is aware of the access barring status of the target cell. The wireless device may also abort handover to a target cell where the handover command indicates that the target cell has enabled access barring. Specifically, the wireless device may abort handover to the target cell if the SIB2 message of the target cell includes access barring information.
For at least these reasons, a CA capable wireless device configured to operate in CA band combination involving FDD and TDD frequency bands which are adjacent or very close to each to each other in frequency domain may degrade or even disrupt operation of other wireless devices operating in these bands. A similar situation also arises if different UL/DL TDD configurations are used in different TDD bands or carriers in the same band, which are adjacent or close to each other (e.g. band 42 and band 43), or where different LTE cells operate in unlicensed bands. A legacy single carrier operation involves both UL and DL transmission in the serving cell of the wireless device. Therefore any legacy single carrier operation in these bands may seriously degrade or even disrupt CA operation.